The invention relates generally to an arrangement for aligning a substrate preparatory to imprinting the substrate with a printed circuit.
More particularly, the invention relates to the alignment of a substrate having locating holes which are designed to receive locating pins.
Screen printing is a conventional technique for applying a printed circuit to a substrate. In order to precisely position the substrate for printing, it has become the practice to provide the substrate with small locating holes which receive locating pins provided in the printing machine. The locating pins, which have a diameter of a few millimeters, are adjusted relative to the printing unit and the substrate is then positioned so that the locating holes are in register with and receive the locating pins.
Although alignment of a substrate by means of locating pins has proved to be highly satisfactory, this procedure poses a problem in automatic machines. The reason is that such machines operate at ever-increasing speeds. Thus, it has been found difficult to rapidly align a substrate in a high-capacity machine using locating holes and cooperating fixed locating pins.
A difficulty which arises is that of inserting the locating pins in the locating holes. This difficulty is due in part to the very small dimensions of the locating pins and locating holes. Furthermore, deformation of the substrate contributes to the difficulty of inserting the locating pins in the locating holes. The substrate undergoes changes in length when it is subjected to temperature fluctuations and this, in turn, causes the relative positions of the locating holes to change.
As a result of the problems associated with insertion of the locating pins in the locating holes, the high output capacity of a modern printing machine cannot be fully utilized. There are continual interruptions in the supply of substrates to, and also in the automatic alignment and fixing of the substrates in, the machine. Moreover, the locating pins are subject to damage which can cause the electronic circuit applied to a substrate by screen printing to be out of register.